1. Field of the Invention
This invention relates to an ion (electron) multiplying device for detecting or measuring energy beams of electrons, ions, charge particles, ultraviolet rays, soft X-rays, etc.
2. Related Background Art
As schematically shown in FIG. 1, in an ion multiplying device, energy beams, as of electrons or others, impinge on dynodes of the ion multiplying unit to multiply and emit secondary electrons, and the collecting electrodes (anodes) A collect the emitted secondary electrons for detection.
The ion multiplying units have various types. Conventional quarter-cylindrical dynodes are substantially alternately arranged in a direction of incidence of energy beams. The arrangement of FIG. 1 is the typical one which is the so-called box-and-grid-type.
Resistors are inserted between the respective dynodes DY and their adjacent ones. The resistors equidivide a voltage applied between a first-stage dynode DY1 and a final-stage dynode DY 16.
This is the basic structure of the ion multiplying units. The general actual assembly of the ion multipliers is shown in FIGS. 2 and 3.
In the ion multiplier of FIGS. 2 and 3, respective dynodes DY are supported, enclosed by respective support frames 1. Each support frame 1 is made of a conducting material and is electrically connected to the associated dynode DY. The ion multiplier further comprises two support rods 3 which are secured to a holder 2 of a thin steel plate and are parallel with each other. These support rods 3 are inserted in holes 4 of each support frame 1 to support the dynodes by the support rods 3. A gap between each support frame 1 and its adjacent one is retained constant by spacers 5 through which the support rods 3 are inserted.
In this conventional ion multiplying device, resistors R are disposed in one row on one of the rows of the dynodes. Leads L of each resistor R are welded respectively to vertically adjacent ones of the support frames 1.
For the measurement of energy beams, as of ions, the above-described ion multiplying device is installed in a vacuum vessel with an energy beam source built in. But it is a problem that when the holder 2 of a thin steel plate is not strong enough to install the device in the vessel. In addition, the dynodes are exposed, and need careful handling.
The installation of the ion multiplying device is followed by drawing air out of the vessel, But the dynodes, which are exposed in the vessel, are subjected to air streams when the air of the vessel is evacuated. Sometimes the air streams contain dust, and the dust sticks to the surfaces of the dynodes, which may cause erroneous measurements. This problem also occurs when, after measurements, the vacuum vessel is released, and air flows into the vessel from the outside. Also in operations in vacuum, oil used in a vacuum pump, sample solvents may be attached onto the surfaces of the dynodes, and as the result, gain of the multiplying device may be degraded.
Furthermore, in some cases energy beams not to be measured, e.g., scattered energy beams, are incident on the sides of the ion multiplying device to enter the exposed dynodes. For analysis of ions of some kinds, plasmas are used, and in some cases, ultraviolet radiation from the plasmas are incident on the dynodes. These energy beams are a cause for noises.